iTunes is one of the best music services providing a platform to organize and enjoy your favorite songs, playlists, albums, artists, movies, TV shows you already have on your local storage. You can also shop for the ones you want to get.
You can also listen to free or on-demand music stations curated by the Apple Music Experts. It comes on macOS and iOS platforms by default, but you can download it on Mac or Windows from its official website.
iTunes is the must if you own an iOS device to sync your data including photos, videos, contacts, music on your iPhone/iPad. The application has easy to use interface with everything shown right on the screen and showing you the list of songs.
It also has the integrated App Store for Apple Devices using which you can download or buy the application on your Apple devices. iTunes is an excellent way of organizing your media files and is best if you use any iOS/macOS device.